Emission control device

ABSTRACT

Lignocellulosic carbonaceous material is activated to produce a high activity, high density gas-phase activated carbon under conditions which effectively alter the particle pore size distribution to optimize the carbon&#39;s mesoporosity. Alternative processes are disclosed for producing the carbon, as are its application in emission control for vehicles.

This application is a division of Ser. No. 839,597, filed Feb. 21, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to activated carbon and methods forpreparing same. Particularly, this invention relates to new carbonsuseful in vapor adsorption and methods for their production. Moreparticularly, this invention relates to activated carbon derived fromlignocellulosic material prepared by chemical activation and shaping toproduce carbon of high density and high activity.

2. Description of the Prior Art

Activated carbon is a microcrystalline, nongraphitic form of carbonwhich has been processed or increase internal porosity. Activatedcarbons are characterized by a large specific surface area typically inthe range of 500-2500 m² /g, which permits its industrial use in thepurification of liquids and gases by the adsorption of gases and vaporsfrom gases and of dissolved or dispersed substances from liquids.Commercial grades of activated carbon are designated as either gas-phaseor liquid-phase adsorbents. Liquid-phase carbons generally may bepowdered, granular, or shaped; gas-phase, vapor-adsorbent carbons arehard granules or hard, relatively dust-free shaped pellets.

Generally, the larger the surface area of the activated carbon, thegreater its adsorption capacity. The available surface area of activatedcarbon is dependent on its pore volume. Since the surface area per unitvolume decreases as individual pore size increases, large surface areais maximized by maximizing the number of pores of very small dimensionsand/or minimizing the number of pores of very large dimensions. Poresizes are defined by the International Union of Pure and AppliedChemistry as micropores (pore width<1.5 nm), mesopores (porewidth=1.2-50 nm), and macropores (pore width>50 nm). Micropores andmesopores contribute to the adsorptive capacity of the activated carbon;whereas, the macropores reduce the density and can be detrimental to theadsorbant effectiveness of the activated carbon, on a carbon volumebasis. The adsorption capacity and rate of adsorption depend to a largeextent upon the internal surface area and pore size distribution.Conventional chemically activated lignocellulose-based carbons generallyexhibit macroporosity (macropore volume) of greater than 20% of thecarbon particle total volume. Gas-phase activated carbon macroporosityof less than 20% of the carbon particle volume would be desirable.Likewise, a high percentage of mesoporosity (i.e., above 50% of totalparticle volume) is desirable.

Commercial activated carbon has been made from material of plant origin,such as hardwood and softwood, corncobs, kelp, coffee beans, rice hulls,fruit pits, nutshells, and wastes such as bagasse and lignin. Activatedcarbon also has been made from peat, lignite, soft and hard coals, tarsand pitches, asphalt, petroleum residues, and carbon black.

Activation of the raw material is accomplished by one of two distinctprocesses: (1) chemical activation, or (2) thermal activation. Theeffective porosity of activated carbon produced by thermal activation isthe result of gasification of the carbon at relatively high temperatures(after an initial carbonization of the raw material), but the porosityof chemically activated products generally is created by chemicaldehydration/condensation reactions occurring at significantly lowertemperatures.

Chemical activation typically is carried out commercially in a singlekiln. The carbonaceous material precursor is impregnated with a chemicalactivation agent, and the blend is heated to a temperature of 450°-700°C. Chemical activation agents reduce the formation of tar and otherby-products, thereby increasing yield.

A "hard active carbon of high adsorptive power in the shaped or mouldedstate" is taught in U.S. Pat. No. 2,083,303 to be prepared byimpregnating pulverized organic raw material, such as "sawdust, peat,lignite or the like" with "known activating agents, such as zincchloride or phosphoric acid" and heated to 100°-200° C. for one to oneand a half hours producing a partially carbonized state wherein thematerial is somewhat plastic. Without reducing the temperature, thematerial is molded under pressure to a desired shape. The shapedmaterial then is activated in a rotary activating retort and brought toa temperature of 450°-600° C. for about four hours.

Similarly, U.S. Pat. No. 2,508,474 teaches a gas mask activated carbonto be prepared by impregnating low density cellulosic material, such asfinely divided wood in the form of wood shavings or sawdust, withconcentrated zinc chloride, and heating to 120°-145° C. while agitatingfor not less than fifty minutes. The reacted mass then is compacted into"forms of appreciable size;" said forms are dried at 160°-300° C.; thedried forms are crushed into granular particles; the granules arecalcined at 675°-725° C.; and, after leaching out of the particles agreater portion of residual zinc chloride, recalcining the activatedcarbon product at 1000°-1100° C. for at least thirty minutes.

These representative techniques have produced activated carbon ofadequate activity and density for many gas-phase applications,especially for purification and separation of gases as in industrial gasstreams, in odor removal in air conditioning systems, and in gas masks.However, older technology gas-phase activated carbons have not provenentirely satisfactory in some applications for recovery (not justremoval) of organic vapors which involves adsorption onto the carbonsurface followed by desorption from the carbon for recapture. In fact,due to environmental concerns and regulatory mandates, one of thelargest single applications for gas-phase carbon is in gasoline vaporemission control canisters on automobiles. Evaporative emissions ventedfrom both fuel tank and carburetor are captured by activated carbon.

Fuel vapors, vented when the fuel tank or carburetor is heated, arecaptured in canisters generally containing from 0.5 to 2 liters ofactivated carbon. Regeneration of the carbon is accomplished by usingintake manifold vacuum to draw air through the canister. The air carriesdesorbed vapor into the engine where it is burned during normaloperation. An evaporative emission control carbon should have suitablehardness, a high vapor working capacity, and a high saturation capacity.The working capacity of a carbon for gasoline vapor is determined by theadsorption-desorption temperature differential, by the volume of purgeair which flows through the carbon canister, and by the extent to whichirreversibly adsorbed, high molecular weight gasoline componentsaccumulate on the carbon.

Because of various economic considerations and space limitations inplacing the carbon canister on-board a vehicle, this particularapplication of granular or shaped activated carbon requires higheractivity and higher density properties than typically produced by theolder technology noted. One method to control product density is taughtby published European Patent Application 0 423 967 A2. The applicantsnote "a number of problems inherent in the use of wood as a raw materialto produce directly a chemically activated pelletised form," claiming itto be "impossible to produce a high density activated carbon from a woodflour material" for lack of sufficient natural binding agent. Animproved product (of substantially increased density) is claimed by useof, as a starting material, a "young carbonaceous vegetable product"having a "high concentration of natural binding agent." Such materialsinclude nut shell, fruit stone and kernel, and in particular olivestone, almond shell, and coconut shell.

Also, U.S. Pat. No. 5,039,651 teaches densification of activated carbonproduct from cellulose materials including coconut shells, wood chips,and sawdust by pressing after initially heating to a relatively lowtemperature, followed by extrusion and calcination. Yet, with thisimproved processing the patentees could produce only carbons that weremeasured to have a volumetric working capacity (in terms of butaneworking capacity, or BWC) of up to 12.3 g/100 cm³, although BWC valuesup to 15 g/100 cm³ are claimed

These prior art gas-phase carbons may have been satisfactory for limitedvolumes of vapors emitted from the carburetor and fuel tank. Because ofimpending environmental regulations requiring capture of greater amountsof fuel vapor emissions, it is anticipated that the volume of theseadditional vapors, combined with the space limitations and economicconsiderations which limit expansion of the size of canister systems,will require activated carbons with higher densities, higher activities,and higher volumetric working capacities than disclosed by the prior art(e.g., BWC>15 g/100 cm³).

Therefore, it is an object of this invention to provide activatedcarbons of high activity and relatively high density suitable forsolvent and vapor capture and recovery. It is a further object of thisinvention to provide chemical activation processes for producing higheractivity gas-phase activated carbons without sacrificing density. Also,it is an object of this invention to employ the high density, highactivity chemically activated carbon for vehicle emission control.

SUMMARY OF THE INVENTION

The above objects of the invention are achieved, unexpectedly, by thechemical activation of a carbonaceous material, preferablylignocellulosic material, with a chemical activation agent in a mannerto produce a plastic intermediate product which is densified toeffectively minimize the macropore structure of the activatedcarbonaceous material. Densification is followed by increasing thetemperature of the shaped product at a controlled rate to from about425° C. to about 650° C.

Alternative novel processes of the invention may be employed dependingon the starting material employed and level of activation desired.Certain processes may be controlled to regulate the degree ofmacroporosity preservation to produce either carbons more suitable forliquid phase applications or carbons more suitable for gas-phaseapplications. The novel high activity, high density gas-phase activatedcarbons produced are characterized by butane working capacities fromabove 15 to about g/100 cm³, preferably from about 17 to about 25 g/100cm³, and more preferably from about 19 to about 25 g/100 cm³, a butaneactivity of from about 50 to about 80 g/100 g, preferably from about 60to about 80 g/100 g, and more preferably from about 70 to about 80 g/100g, and a density of from about 0.25 to about 0.40 g/cm³, preferably fromabout 0.27 to about 0.40 g/cm³, more preferably from about 0.30 to about0.40 g/cm³.

Preferably, such an activated carbon material also would exhibit amesopore content of greater than about 50%, preferably greater thanabout 60%, and more preferably greater than about 70%, based on thetotal particle volume, and a macropore content of less than 20%,preferably less than 18%, an more preferably less than 15%, based on thetotal particle volume.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The raw material precursor in the invention chemical activation may beany of the carbonaceous material of plant or mineral origin earlierrecited. Preferred precursors primarily are lignocellulosic materials ofplant origin and include wood-based materials such as wood chips, woodflour, and sawdust, as well as nut pits and nut shells such as coconutshell. Chemical activation agents may include alkali metal hydroxides,carbonates, sulfides, and sulfates; alkaline earth carbonates,chlorides, sulfates, and phosphates; phosphoric acid; polyphosphoricacid; pyrophosphoric acid; zinc chloride; sulfuric acid; and oleum.Preferred among these are phosphoric acid and zinc chloride. Mostpreferred is phosphoric acid.

The invention methods for producing the novel carbon can be describedgenerally by the following sequence of steps:

1. Activating agent/lignocellulose material blending

2. Stage 1 heat treatment (plasticization)

3. Shaping and densifying

4. Stage 2 heat treatment (thermosetting)

5. Activation

The activation typically occurs in a rotary kiln in which thetemperature of the thermoset shaped mixture is raised to about 550° C.This basic process normally is followed with washing and drying steps.

One particular method for producing the invention activated carbonproduct (Process A) involves blending a 1:3-1:1 mixture respectively ofa chemical activating agent, preferably phosphoric acid or zincchloride, with a lignocellulose material, preferably wood chips, sawdust(or, wood dust), or wood flour, with agitation for up to one hour at atemperature of from about 35° C. to about 95° C., after which themixture is spread on a flat surface in layers of a thickness of fromabout 6 mm to about 25 mm. The mixture is subjected to a first stageheat treatment at a temperature of from about 35° C. to about 95° C. fora time sufficient that the mixture material goes through a transitionfrom a highly plastic phase to begin to thermoset. Then the material issubjected to a densification step which involves processing through acompressive shaping device such as an extruder or a Marumerizer. Thenthe shaped material is heat treated again (second stage) at from about35°0 C. to about 95° C. to complete the densification by completing thethermosetting process. Upon complete elimination of plasticity, thetemperature is gradually increased to from about 425° C. to about 650°C.

Typical product characteristics resulting from this process are shown inTable I.

                  TABLE I                                                         ______________________________________                                        Invention Activated Carbon Product Characteristics                            ______________________________________                                        Butane Working Capacity                                                                             17.7 g/100 cm.sup.3                                     Butane Activity       68.0 g/100 g                                            Surface Area          2180 m.sup.2 /g                                         Apparent Density      0.30 g/cm.sup.3                                         Particle Density      0.46 g/cm.sup.3                                         Mesopore Content      58%                                                     Macropore Content     12%                                                     ______________________________________                                    

The surprising improvement in butane working capacity of the new carbonproduct reflects a major increase in mesoporosity of the individualcarbon particles, at the expense of macroporosity.

A standard determination of surface area of activated carbon usually isby the Brunauer-Emmett-Teller (BET) model of physical adsorption usingnitrogen as the adsorptive. This was the method employed in calculatingthe invention carbon surface areas, based on nitrogen adsorptionisotherm data in the range of 0.05 to 0.20 relative pressure.

In the case of granular activated carbon, the density is an importantfeature of the effectiveness of the adsorbent, a many applications ofgranular or shaped activated carbon involve a static active carbon bedof fixed volumetric size. The apparent density of the inventionactivated carbon is measured according to the method ASTM D 2854.Measurements of apparent density of carbon in a packed bed of particlesreported herein were based on 10×25 mesh carbon materials.

The density of the individual carbon particles was determined bydisplacement of mercury using a Micromeritics® PoreSizer 9310instrument. The density is based on the mass of a particle and itsvolume including pores smaller than 35 micrometers.

Butane activity of the invention carbons was calculated by placing aweighed sample of the dry activated carbon, approximately 15 ml involume, in a 1.45 cm diameter tube and admitting butane gas therein. Theamount adsorbed at saturation at 25° C. is weighed and reported asbutane activity in grams of butane per 100 grams carbon (g/100 g). Thetube then is purged with air at 25° C. at 250 ml/min. for 40 minutes,and the amount of butane removed is reported as butane working capacity(BWC) in grams of butane per 100 ml of carbon (g/100 cm³). The carbonmass to volume conversion is made on the basis of the measured value ofthe carbon apparent density. In view of the interrelationship of butaneactivity, BWC, and density, for carbons of a density from about 0.25 toabout 0.40 g/cm³, a BWC >15 can be achieved with butane activity valuesof at least about 50 g/100 g.

Porosity in pores larger than 50 nm (macroporosity) was determined usinga Micromeritics® PoreSizer 9310 which measures the volume of mercuryforced into pores under the influence of pressure. The distribution ofpore volume with pore size is calculated using the washburn equation, astandard model.

Porosity in pores smaller than 50 nm was determined using aMicromeritics® DigiSorb 2600 Adsorption isotherm data for nitrogen,measured at a temperature of about 77° K., are used with the Kelvin andHalsey equations to determine the distribution of pore volume with poresize of cylindrical pores according to the standard model of Barrett,Joyner, and Halenda. For the purposes of the examples and the inventionclaimed herein, macroporosity consists of pore diameters greater than 50nm, mesoporosity consists of pore diameters of from 1.8 to 50 nm, andmicroporosity consists of pore diameters of less than 1.8 nm.

In an alternative method (Process B), after the blending and stage 1heat treatment steps as above, the critical steps of shaping anddensification are achieved in a high-speed mixer/agglomerator such as apin-mixer where particles of plastic char with a high density areformed. Formed granules must be heat treated further as provided in theearlier discussed process to obtain strong bonding and, consequently, tomaintain the particle strength.

Activated carbon prepared according to this process exhibited a butaneworking capacity of 18.1 g/100 cm³, an apparent density of 0.29 g/cm³, aparticle density of 0.48 g/cm³, a mesopore volume of 60%, and amacropore volume of 12%.

Another method for producing novel activated gas-phase carbon of highdensity and high activity (Process C) involves reducing themacroporosity of the activated carbon product by blending the activatingagent and lignocellulose material under conditions (of temperature andacid concentration of the activating agent) such that the lignocellulosematerial is substantially degraded (i.e., solubilized). For example,solubilization of wood with phosphoric acid produces a viscous fluid inwhich the discrete particles of the original lignocellulose can nolonger be identified. In the solubilization process, the initialviscosity of the slurry mixture is very close to that of the phosphoricacid alone. As the temperature rises, the viscosity of the massincreases as the wood elements thereof dissolve. If the viscosityincreases too fast during this stage 1 heat treatment, water can beadded to maintain sufficient fluidity for continued mixing under heat atfrom about 80° C. to about 120° C. Upon reaching transition from plasticto initial thermoset, the material is subjected to shaping, stage 2 heattreatment, and activation steps as described in Process A.

The foregoing methods are capable of producing the invention highactivity, high density activated carbon from relatively low densitylignocellulose materials, such as wood chips, wood flour, and sawdust Analternative variation of the invention method to achieve a high densityactivated carbon employs a higher density starting material, such ascoconut shell (Process D). This alternative process differs from thepreviously discussed methods in that the stage 1 heat treatment andshaping steps are eliminated. This process also differs from prior artmethods of activating coconut shell and produces novel activated carbonproducts as a result of the combined use of extended time at lowtemperature during heat treatment, drying, and thermoset, and, similarto Processes A-C, activation at a gradual heat up rate to a finaltemperature of about 480° C. Due to its natural density, conventionalactivation of coconut shell results in activated carbon material withhigh microporosity and mesoporosity and low macroporosity. Thus, theimprovement in adsorption capacity resulting in a novel activated carbonis achieved by the invention process by creating higher mesoporosity.

Alternative novel methods for producing the invention activated carbonproduct are disclosed in the following examples.

EXAMPLE 1

A series of seven batches of activated carbon products of Process A wasprepared by mixing 2,070 g of concentrated phosphoric acid solution(85-86% concentration) with 1,950 g of sawdust (43% moisture) for anacid:sawdust ratio of 1.6:1 (by dry weight of their respective solids)and stirring for 30 minutes at 80°-95° C., after which the mixture (amass of discreet sawdust particles) was transferred to shallow glasstrays and spread into 1-1.5 cm thick layers for continued heating in anoven. Heat treatment was continued at 70° C. for about 36 hours, atwhich time the material began transition from plastic to thermoset(i.e., product appears dry and not sticky but is nevertheless softenough to be shaped in the Marumerizer). Upon shaping by processing inthe Marumerizer (residence time of 15-30 minutes at 800 rpm), theindividual sawdust particles are formed into smooth beads. The shapedproduct is returned to the oven for continued heating at 85° C. forabout 36 hours to complete the thermosetting process.

Activation of the thermoset char was performed in a bench-scale,direct-fired rotary kiln by gradually raising the temperature to about480° C.

The seven batches of carbon yielded butane working capacity valuesranging from 16.1 g/100 cm³ to 18.2 g/100 cm³. The properties of theseactivated carbon products are listed in Table II.

                  TABLE II                                                        ______________________________________                                        Activated Carbon Properties                                                                          Butane   Apparent                                      Sample   BWC           Activity Density                                       No.      g/100 cm.sup.3                                                                              g/100 g  g/cm.sup.3                                    ______________________________________                                        1        16.7          67.2     0.28                                          2        17.3          64.4     0.30                                          3        18.2          68.8     0.30                                          4        16.2          63.6     0.28                                          5        17.1          66.6     0.29                                          6        16.1          63.8     0.29                                          7        18.1          69.0     0.30                                          ______________________________________                                    

EXAMPLE 2

A 1.3 liter sample having a BWC of 17.7 g/100 cm³ was prepared forgasoline vapor adsorption testing by combining product of sample nos. 3,5, and 7 from Example 1. In this test a 375 ml sample of activatedcarbon in a test canister is challenged with gasoline vapor generated bybubbling 200 ml/min of air through 300 ml of gasoline at a temperatureof 30° C. The vapor is adsorbed on the carbon and at saturationbreakthrough is detected with a total hydrocarbon analyzer at aconcentration of about 5000 ppm. After breakthrough, a countercurrentflow of air is admitted at a rate of 7.5 ml/min for 10 minutes to desorbthe gasoline vapor. The adsorption/desorption steps are continued for 25cycles. The gasoline working capacity (GWC) is calculated as the averagemass of vapor adsorbed during cycles 21-25, expressed on a carbon volumebasis. The test showed a capacity of 61 g/l, which compares to a 50 g/lfor commercial WV-A 1100.

Also, pore size distribution of this sample combination was determinedby using mercury intrusion and nitrogen adsorption. Analysis of thisdata indicates that mechanical action in the Marumerizer substantiallydecreased the macropore (>50 nm) volume of the product. An increase inthe large mesopore (5-50 nm) suggests that some kind of squeezing actiontook place, but there was, nevertheless, a net reduction in porosityoutside the small mesopore range (important for butane workingcapacity), which translates to an increase in effective density. TableIII compares the invention carbon with commercial WV-A 1100 in terms ofbutane capacity and porosity.

                                      TABLE III                                   __________________________________________________________________________                            PERCENT OF PARTICLE VOLUME                                  BACT BWC  Ad  PD  >50 nm                                                                             5-50 nm                                                                              1.8-5 nm                                                                            <1.8 nm                             Carbon                                                                              g/100 g                                                                            g/100 ml                                                                           gm/ml                                                                             gm/ml                                                                             Macro                                                                              Large Meso                                                                           Small Meso                                                                          Micro                               __________________________________________________________________________    WV-A 1100                                                                           47.3 11.8 .28 .48 23    9     38    6                                   Invention                                                                           68.0 17.7 .30 .46 12   12     46    8                                   __________________________________________________________________________

EXAMPLE 3

An activated carbon product of Process A was prepared by blending 2235 gof phosphoric acid solution (86% concentration) with 2069 g of 4×14 mesh(U.S.) wood chips (42% moisture, produced using a rotary drum chipper)for an acid:wood ratio of 1.6:1. The mixture was stirred for 60 minutesat 50° C. after which it was transferred to shallow glass trays for heattreatment in an oven at about 120° C. for 45 minutes. Following thisinitial heat treatment, the mixture was transferred to an oven andheated at about 140° C. for 30 minutes. The plastic char, which retainedthe discrete nature of the wood chips, was processed in a Marumerizerfor 30 minutes to partially shape and densify it, but withoutsubstantially changing its granular nature. Then it was transferred toan oven to complete the thermosetting process by heating it at 85° C.for 16 hours. The thermoset char was activated by raising itstemperature to about 480° C., using a direct-fired, rotary kiln. Theactivated char was washed with water to remove the residual acid and thegranular activated carbon product evaluated, yielding the followingproduct property values:

                  TABLE IV                                                        ______________________________________                                        Butane Working Capacity:                                                                            15.8 g/100 cm.sup.3                                     Apparent Density      0.26 g/cm.sup.3                                         Butane Activity       68.2 g/100 cm.sup.3                                     Particle Density      0.43 g/cm.sup.3                                         Surface Area          2490 m.sup.2 /g                                         Macropore Content     19%                                                     Mesopore Content      54%                                                     ______________________________________                                    

EXAMPLE 4

An activated carbon product of Process B was prepared by combining 2,000g of aqueous 86% concentration phosphoric acid solution with 1,900 g ofwet sawdust (for an acid:sawdust ratio of 1.6:1) and blending same in amechanical mixer for 10 minutes at room temperature. The mixture washeated in an oven at 177° C. for 45 minutes and then dried in a steamoven at 177° C. for 45 minutes, with stirring at 15 minute intervals.The plastic char mixture, in an amount of 2.7 liters, was fed into abatch pin-mixer rotating at 1,000 rpm, and 100 ml water was added. Thisnow granular char was densified into particles of about 10×25 mesh(0.7-2.0 mm) in size in about 5 minutes. The shaped char was thermosetin an oven at 82° C. for 60 hours. Subsequently, the char was activatedby heating to 480° C. in about 60 minutes in a direct-fired rotary kiln.The activated product was washed with water and evaluated. The measuredproduct properties were compared with measured properties of commercialWV-A 1100 as presented in Table V.

                  TABLE V                                                         ______________________________________                                        Product Properties                                                                            Process B   WV-A 1100                                         ______________________________________                                        Butane Working Capacity                                                                       18.1 g/100 cm.sup.3                                                                       11.8 g/100 cm.sup.3                               Butane Activity 69.7 g/100 g                                                                              47.3 g/100 g                                      Apparent Density                                                                              0.29 g/cm.sup.3                                                                           0.28 g/cm.sup.3                                   Particle Density                                                                              0.48 g/cm.sup.3                                                                           0.48 g/cm.sup.3                                   Macropore Volume                                                                              12%         23%                                               Mesopore Volume 60%         47%                                               Surface Area    2420 m.sup.2 /g                                                                           1840 m.sup.2 /g                                   ______________________________________                                    

EXAMPLE 5

An activated carbon product of Process C was prepared by heating 698 gof 86% phosphoric acid to 105° C. Sawdust in a total amount of 300 g(dry basis) was added (causing the acid temperature to drop) and mixedas the temperature of the mixture was raised to 75° C. Mixing continuedfor 57 minutes with periodic addition of sufficient water to maintainfluidity. The viscous fluid product then was transferred to glass traysand heat treated at a temperature of 120° C. for 16 hours. The resultantsolidified product was granulated and the granules were processed in aMarumerizer for 13 minutes converting them to smooth, spheroidalparticles. Finally, this product was activated in a direct fired, rotarykiln by heating to 480° C. The resultant activated carbon had thefollowing product properties:

                  TABLE VI                                                        ______________________________________                                        Butane Working Capacity                                                                             17.6 g/100 cm.sup.3                                     Butane Activity       71.8 g/100 g                                            Apparent Density      0.29 g/cm.sup.3                                         Particle Density      0.46 g/cm.sup.3                                         Macropore Content     13%                                                     Mesopore Content      55%                                                     Surface Area          2260 m.sup.2 /g                                         ______________________________________                                    

EXAMPLE 6

An activated carbon product of Process D was prepared by mixing 400 g of8×20 mesh coconut shell (12.7% moisture) and 660 g of 86% concentrationphosphoric acid for 10 minutes. The mixture then was heat treated inthree phases. Spread in a thin layer (13 mm thick), the mixture washeated in an oven at 65°-70° C. for 8 hours with stirring at 30 minuteintervals, then an additional 16 hours without stirring. In the secondphase, the oven temperature was raised to 95°-100° C. for 8 hours withstirring at 30 minute intervals, then an additional 16 hours withoutstirring. Finally, the oven temperature was increased to 120° C. for 2hours, after which the mixture was removed.

This heat treated char was activated in a direct fired laboratory rotarykiln under an atmosphere of air and flue gases from a natural gasburner. The kiln temperature was raised from 30° C. to 480° C. Aftercooling, the activated material was washed and dried in a tray dryingoven. The results of analyses conducted of the product are:

                  TABLE VII                                                       ______________________________________                                        Butane Activity       63.6 g/100 g                                            Butane Working Capacity                                                                             16.7 g/100 cm.sup.3                                     Apparent Density      0.30 g/cm.sup.3                                         Particle Density      0.50                                                    Macropore Content     12%                                                     Mesopore Content      55%                                                     Surface Area          2260 m.sup.2 /g                                         ______________________________________                                    

EXAMPLE 7

In a modification of the Process A, as applied in Example 1, sawdust wasmixed with phosphoric acid, and the mixture was heat treated until thematerial began a transition from plastic to a thermoset state. Then theheat treated material was subjected to a mechanical pressing (new step)by passing it between two closely spaced rollers. The resultantcompressed material was granulated and processed in a Marumerizer forabout 30 minutes. Subsequent heat treatment and activation wereperformed as in Example 1. The suprising result of the mechanicalpressing step is that it increases the butane activity of the productand, in conjunction therewith, also raises the butane working capacity.The properties of the product are as shown in Table VIII.

                  TABLE VIII                                                      ______________________________________                                        Butane Working Capacity                                                                             19.2 g/100 cm.sup.3                                     Butane Activity       72.5 g/100 g                                            Apparent Density      0.30 g/cm.sup.3                                         Particle Density      0.47 g/cm.sup.3                                         Macropore Content     12%                                                     Mesopore Content      62%                                                     Surface Area          2480 m.sup.2 /g                                         ______________________________________                                    

In each of the above examples, activated carbon of surprisingly highbutane working capacity is produced by increasing surface area withoutsacrificing material density. This has been achieved by increasingcarbon particle mesoporosity. In most instances the increase inmesoporosity has been created while simultaneously reducing the carbonparticle's macroporosity.

While the invention high activity, high density carbon has beendescribed and illustrated herein by references to various specificmaterials, procedures, and examples, it is understood that the inventionis not restricted to the particular materials, combinations ofmaterials, and procedures selected for that purpose. With the disclosureherein of the concepts employed to produce the novel carbon, numerousvariations of such details can be employed, as will be appreciated bythose skilled in the art.

What is claimed is:
 1. An evaporative emission control device foradsorbing gasoline vapors comprising a high activity, high density,lignocellulose-based activated carbon characterized by a butane activityof from about 50 to about 80 g/100 g, a butane working capacity of fromabove 15 to about 25 g/100 cm³, an apparent density of from about 0.25to about 0.40 g/cm³, greater than about 50% of total carbon particlevolume comprising pores of a width from about 1.8 to about 50 nm, andless than about 20% of total carbon particle volume comprising pores ofa width greater than about 50 nm.
 2. The evaporative emission controldevice of claim 1 wherein the butane working capacity is from about 17to about 25 g/100 cm³.
 3. The evaporative emission control device ofclaim 2 wherein the butane working capacity is from about 19 to about 25g/100 cm³.
 4. An improved method for controlling emission of fuel vaporsfrom vehicles by routing said vapors from the vehicle fuel tank to acarbon-containing emission control device wherein the improvementcomprises carbon which is lignocellulose-based, high activity and highdensity activated carbon particulate characterized by a butane activityfrom about 50 to about 80 g/100 g, an apparent density of from about0.25 to about 0.40 g/cm³, a butane working capacity of from above 15 to25 g/100 cm³, and wherein greater than about 50% of total carbonparticle volume comprises pores of a width from about 1.8 to about 50nm, and less than about 20% of total carbon particle volume comprisingpores of a width greater than about 50 nm.
 5. The improved method ofclaim 4 wherein the butane working capacity is from about 17 to about 25g/100 cm³.
 6. The improved method of claim 5 wherein the butane workingcapacity is from about 19 to about 25 g/100 cm³.